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From: David Woodhouse <dwmw2@infradead.org>
To: Joao Martins <joao.m.martins@oracle.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: "Ankur Arora" <ankur.a.arora@oracle.com>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org
Subject: Re: [PATCH RFC 10/39] KVM: x86/xen: support upcall vector
Date: Wed, 02 Dec 2020 11:17:32 +0000	[thread overview]
Message-ID: <71753a370cd6f9dd147427634284073b78679fa6.camel@infradead.org> (raw)
In-Reply-To: <20190220201609.28290-11-joao.m.martins@oracle.com>

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On Wed, 2019-02-20 at 20:15 +0000, Joao Martins wrote:
> @@ -176,6 +177,9 @@ int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
>         int r;
>  
>         switch (e->type) {
> +       case KVM_IRQ_ROUTING_XEN_EVTCHN:
> +               return kvm_xen_set_evtchn(e, kvm, irq_source_id, level,
> +                                      line_status);
>         case KVM_IRQ_ROUTING_HV_SINT:
>                 return kvm_hv_set_sint(e, kvm, irq_source_id, level,
>                                        line_status);
> @@ -325,6 +329,13 @@ int kvm_set_routing_entry(struct kvm *kvm,
>                 e->hv_sint.vcpu = ue->u.hv_sint.vcpu;
>                 e->hv_sint.sint = ue->u.hv_sint.sint;
>                 break;
> +       case KVM_IRQ_ROUTING_XEN_EVTCHN:
> +               e->set = kvm_xen_set_evtchn;
> +               e->evtchn.vcpu = ue->u.evtchn.vcpu;
> +               e->evtchn.vector = ue->u.evtchn.vector;
> +               e->evtchn.via = ue->u.evtchn.via;
> +
> +               return kvm_xen_setup_evtchn(kvm, e);
>         default:
>                 return -EINVAL;
>         }


Hmm. I'm not sure I've have done it that way.

These IRQ routing entries aren't for individual event channel ports;
they don't map to kvm_xen_evtchn_send().

They actually represent the upcall to the given vCPU when any event
channel is signalled, and it's really per-vCPU configuration.

When the kernel raises (IPI, VIRQ) events on a given CPU, it doesn't
actually use these routing entries; it just uses the values in
vcpu_xen->cb.{via,vector} which were cached from the last of these IRQ
routing entries that happens to have been processed?

The VMM is *expected* to set up precisely one of these for each vCPU,
right? Would it not be better to do that via KVM_XEN_HVM_SET_ATTR?

The usage model for userspace is presumably that the VMM should set the
appropriate bit in evtchn_pending, check evtchn_mask and then call into
the kernel to do the set_irq() to inject the callback vector to the
guest?

I might be more inclined to go for a model where the kernel handles the
evtchn_pending/evtchn_mask for us. What would go into the irq routing
table is { vcpu, port# } which get passed to kvm_xen_evtchn_send().

Does that seem reasonable?

Either way, I do think we need a way for events raised in the kernel to
be signalled to userspace, if they are targeted at a vCPU which has
CALLBACK_VIA_INTX that the kernel can't do directly. So we probably
*do* need that eventfd I was objecting to earlier, except that it's not
a per-evtchn thing; it's per-vCPU.



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  reply	other threads:[~2020-12-02 11:18 UTC|newest]

Thread overview: 126+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-20 20:15 [PATCH RFC 00/39] x86/KVM: Xen HVM guest support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 01/39] KVM: x86: fix Xen hypercall page msr handling Joao Martins
2019-02-22  1:30   ` Sean Christopherson
2019-02-22 11:47     ` Joao Martins
2019-02-22 12:51     ` Paolo Bonzini
2020-11-30 10:39       ` David Woodhouse
2020-11-30 11:03         ` Paolo Bonzini
2020-11-30 11:27           ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 02/39] KVM: x86/xen: intercept xen hypercalls if enabled Joao Martins
2019-02-21 18:29   ` Sean Christopherson
2019-02-21 20:56     ` Joao Martins
2019-02-22  0:30       ` Sean Christopherson
2019-02-22 12:50         ` Paolo Bonzini
2020-12-01  9:48   ` David Woodhouse
2020-12-01 11:19     ` David Woodhouse
2020-12-02 11:17       ` Joao Martins
2020-12-02 12:12         ` David Woodhouse
2020-12-02  5:19     ` Ankur Arora
2020-12-02  8:03       ` David Woodhouse
2020-12-02 18:20         ` Ankur Arora
2019-02-20 20:15 ` [PATCH RFC 03/39] KVM: x86/xen: register shared_info page Joao Martins
2020-12-01 13:07   ` David Woodhouse
2020-12-02  0:40     ` Ankur Arora
2020-12-02  1:26       ` David Woodhouse
2020-12-02  5:17         ` Ankur Arora
2020-12-02 10:50           ` Joao Martins
2020-12-02 10:44       ` Joao Martins
2020-12-02 12:20         ` David Woodhouse
2020-12-02 20:32           ` Ankur Arora
2020-12-03 10:16             ` David Woodhouse
2020-12-04 17:30               ` Sean Christopherson
2020-12-02 20:33         ` Ankur Arora
2020-12-12 12:07       ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 04/39] KVM: x86/xen: setup pvclock updates Joao Martins
2019-02-20 20:15 ` [PATCH RFC 05/39] KVM: x86/xen: update wallclock region Joao Martins
2019-02-20 20:15 ` [PATCH RFC 06/39] KVM: x86/xen: register vcpu info Joao Martins
2019-02-20 20:15 ` [PATCH RFC 07/39] KVM: x86/xen: register vcpu time info region Joao Martins
2019-02-20 20:15 ` [PATCH RFC 08/39] KVM: x86/xen: register steal clock Joao Martins
2019-02-20 20:15 ` [PATCH RFC 09/39] KVM: x86: declare Xen HVM guest capability Joao Martins
2019-02-20 20:15 ` [PATCH RFC 10/39] KVM: x86/xen: support upcall vector Joao Martins
2020-12-02 11:17   ` David Woodhouse [this message]
2020-12-02 13:12     ` Joao Martins
2020-12-02 16:47       ` David Woodhouse
2020-12-02 18:34         ` Joao Martins
2020-12-02 19:02           ` David Woodhouse
2020-12-02 20:12             ` Joao Martins
2020-12-02 20:37               ` David Woodhouse
2020-12-03  1:08             ` Ankur Arora
2020-12-08 16:08             ` David Woodhouse
2020-12-09  6:35               ` Ankur Arora
2020-12-09 10:27                 ` David Woodhouse
2020-12-09 10:51                   ` Joao Martins
2020-12-09 11:39                     ` David Woodhouse
2020-12-09 13:26                       ` Joao Martins
2020-12-09 15:41                         ` David Woodhouse
2020-12-09 16:12                           ` Joao Martins
2021-01-01 14:33           ` David Woodhouse
2021-01-05 12:11             ` Joao Martins
2021-01-05 13:23               ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 11/39] KVM: x86/xen: evtchn signaling via eventfd Joao Martins
2020-11-30  9:41   ` David Woodhouse
2020-11-30 12:17     ` Joao Martins
2020-11-30 12:55       ` David Woodhouse
2020-11-30 15:08         ` Joao Martins
2020-11-30 16:48           ` David Woodhouse
2020-11-30 17:15             ` Joao Martins
2020-11-30 18:01               ` David Woodhouse
2020-11-30 18:41                 ` Joao Martins
2020-11-30 19:04                   ` David Woodhouse
2020-11-30 19:25                     ` Joao Martins
2021-11-23 13:15           ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 12/39] KVM: x86/xen: store virq when assigning evtchn Joao Martins
     [not found]   ` <b750291466f3c89e0a393e48079c087704b217a5.camel@amazon.co.uk>
2022-02-10 12:17     ` Joao Martins
2022-02-10 15:23       ` [EXTERNAL] " David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 13/39] KVM: x86/xen: handle PV timers oneshot mode Joao Martins
2019-02-20 20:15 ` [PATCH RFC 14/39] KVM: x86/xen: handle PV IPI vcpu yield Joao Martins
2019-02-20 20:15 ` [PATCH RFC 15/39] KVM: x86/xen: handle PV spinlocks slowpath Joao Martins
2022-02-08 12:36   ` David Woodhouse
2022-02-10 12:17     ` Joao Martins
2022-02-10 14:11       ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 16/39] KVM: x86: declare Xen HVM evtchn offload capability Joao Martins
2019-02-20 20:15 ` [PATCH RFC 17/39] x86/xen: export vcpu_info and shared_info Joao Martins
2019-02-20 20:15 ` [PATCH RFC 18/39] x86/xen: make hypercall_page generic Joao Martins
2019-02-20 20:15 ` [PATCH RFC 19/39] xen/xenbus: xenbus uninit support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 20/39] xen-blkback: module_exit support Joao Martins
2019-02-25 18:57   ` Konrad Rzeszutek Wilk
2019-02-26 11:20     ` Joao Martins
2019-02-20 20:15 ` [PATCH RFC 21/39] KVM: x86/xen: domid allocation Joao Martins
2019-02-20 20:15 ` [PATCH RFC 22/39] KVM: x86/xen: grant table init Joao Martins
2019-02-20 20:15 ` [PATCH RFC 23/39] KVM: x86/xen: grant table grow support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 24/39] KVM: x86/xen: backend hypercall support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 25/39] KVM: x86/xen: grant map support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 26/39] KVM: x86/xen: grant unmap support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 27/39] KVM: x86/xen: grant copy support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 28/39] KVM: x86/xen: interdomain evtchn support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 29/39] KVM: x86/xen: evtchn unmask support Joao Martins
2019-02-20 20:16 ` [PATCH RFC 30/39] KVM: x86/xen: add additional evtchn ops Joao Martins
2019-02-20 20:16 ` [PATCH RFC 31/39] xen-shim: introduce shim domain driver Joao Martins
2019-02-20 20:16 ` [PATCH RFC 32/39] xen/balloon: xen_shim_domain() support Joao Martins
2019-02-20 20:16 ` [PATCH RFC 33/39] xen/grant-table: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 34/39] xen/gntdev: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 35/39] xen/xenbus: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 36/39] drivers/xen: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 37/39] xen-netback: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 38/39] xen-blkback: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 39/39] KVM: x86: declare Xen HVM Dom0 capability Joao Martins
2019-02-20 21:09 ` [PATCH RFC 00/39] x86/KVM: Xen HVM guest support Paolo Bonzini
2019-02-21  0:29   ` Ankur Arora
2019-02-21 11:45   ` Joao Martins
2019-02-22 16:59     ` Paolo Bonzini
2019-03-12 17:14       ` Joao Martins
2019-04-08  6:44         ` Juergen Gross
2019-04-08 10:36           ` Joao Martins
2019-04-08 10:42             ` Juergen Gross
2019-04-08 17:31               ` Joao Martins
2019-04-09  0:35                 ` Stefano Stabellini
2019-04-10  5:50                   ` [Xen-devel] " Ankur Arora
2019-04-10 20:45                     ` Stefano Stabellini
2019-04-09  5:04                 ` Juergen Gross
2019-04-10  6:55                   ` Ankur Arora
2019-04-10  7:14                     ` Juergen Gross
2019-02-20 23:39 ` [Xen-devel] " Marek Marczykowski-Górecki
2019-02-21  0:31   ` Ankur Arora
2019-02-21  7:57   ` Juergen Gross
2019-02-21 12:00     ` Joao Martins
2019-02-21 11:55   ` Joao Martins

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